1. Field of the Invention
This invention relates to a pressure sensor for measuring the pressure of fluids at cryogenic temperatures under magnetic fields.
2. Prior Art Statement
Recent years have seen increased use of magnetic fields in a wide range of disciplines. Behind this has been the advances made in superconducting magnet technology. While superconducting magnets are able to conduct current at zero electrical resistance, they have to be cooled to cryogenic temperatures in order to function. Liquid helium is used as the cooling medium.
In order to ensure reliable operation of a cooling system using such a cooling medium, it is indispensable to be able to measure the pressure of the cooling medium at cryogenic temperatures (down to a few degrees K). Since no pressure sensor reliable at cryogenic temperatures was available, however, the ordinary practice was to use a capillary for conducting the pressure from the cryogenic temperature region to a room temperature region and measuring it there with a room temperature pressure measurement system.
This conventional method of pressure measurement via a capillary exhibits poor response, however, because a time delay arises owing to the time required for the medium to travel from the cryogenic temperature region to the room temperature pressure measurement system. In addition, where the pressure within a closed volume that expands and contracts at cryogenic temperatures is measured, accurate measurement becomes impossible because the volume of the capillary is added to the compressed volume of the cooling system. Moreover, there is also a possibility that heat traveling along the capillary from the room temperature region to the cryogenic temperature region may place an excessive heat load on the refrigeration equipment of the cooling system.
All of these problems would be eliminated if it were possible to measure the pressure of the cooling medium with a pressure sensor located in the low temperature region. To enable such measurement, the pressure sensor would have to be able to operate under cryogenic temperatures, to be compact, to produce little heat during measurement, and, when used to measure the pressure of the cooling medium of a superconducting magnet, to be capable of conducting the measurement without influence from the magnetic field.
The present invention was accomplished to overcome the aforesaid problems and has as its object to provide a compact pressure sensor for fluids capable of operating accurately at cryogenic temperatures substantially unaffected by magnetic fields.